1. Field Of The Invention
This invention relates generally to crossed roller bearings, and more particularly to a low-friction crossed roller bearing with a load-bearing cage structure.
2. Description Of The Related Art
Crossed roller bearings reduce friction between two rotating bodies and can withstand axial, radial, and moment loads, providing the advantages of multiple row bearings in the space of a single row bearing. FIG. 1 shows a typical conventional crossed roller bearing 10 of a type shown, for example, in U.S. Pat. No. 2,628,137 to Ashton. The bearing comprises an outer ring 12 and an adjacent inner ring 14. The inner ring is split for easier assembly of the bearing and is comprised of a top half 16 and a bottom half 18. The adjacent, facing surfaces of the outer ring and inner ring are provided with V-shaped grooves whose surfaces define bearing races. The outer ring includes an upper race 20 and a lower race 22. The inner ring includes an upper race 24 and a lower race 26. The races define an annular space between the rings that is filled with a plurality of rollers 28.
The rollers 28 are of a tapered cylindrical shape, having axial end surfaces 30, 31 and conical longitudinal peripheral surfaces 32. The rollers are separated and kept rolling through low-load areas by a cage structure 34. Individual spacers in the shape of blocks or disks are also used, for example, as shown by U.S. Pat. No. 3,275,391 to Blais. The tapered shape of the rollers dictates that one outwardly facing axial end surface 30 has a larger diameter than the other end surface 31. The rollers are alternatingly inclined, or crossed. That is, the axial orientation of the rollers 28 alternates by approximately 90 degrees between adjacent rollers, as illustrated in FIG. 1. The bearing 10 reduces the friction between two rotating bodies through relative movement between the outer ring 12 and the inner ring 14. During this movement, the rollers will rotate about their longitudinal axes in the annular space between the rings. Bearing loads are reacted against the races by the rollers. Because the rollers are tapered, the loads from the races create a resultant force that tends to move the rollers outwardly in a direction perpendicular to the larger diameter axial end surface 30. This is referred to as end loading of the rollers.
When a roller belonging to one set of inclined rollers rotates, its peripheral surface 32 rolls along the upper, outer race 20 and lower inner race 26. The larger diameter axial end surface 30 of the roller is pressed against the other outer race 22 and is essentially dragged along the race surface. That is, the larger diameter axial end surface will be in sliding contact with the outer race as the roller rolls within the annular space. The alternately inclined set of rollers will have rolling contact with the opposite corresponding races 22 and 24, and will have sliding contact with the other outer race 20. Thus, the outwardly directed force from the rollers that results from bearing loads presses the large diameter axial end surface against the outer race.
The end loading and resultant sliding contact of the roller axial end surfaces on the races produces friction and limits the bearing speed. The friction also generates heat and increases the wear of the races. Because of the increased friction and wear, crossed roller bearings are typically limited to low speed applications on the order of 500 rpm or less. It is also generally more difficult to keep conventional crossed roller bearings lubricated when compared with other roller bearing designs, further dictating low speed applications. The problems of end loading have been recognized, but thus far efforts have only resulted in a reduction of the sliding contact with the races, rather than a complete elimination. See, for example, U.S. Pat. No. 3,361,501 to Messinger et al. and U.S. Pat. No. 4,746,232 to Gugel.
Thus, there is a need for a crossed roller bearing that can withstand axial, radial, and moment loads in a compact size, while eliminating sliding contact of the rollers with the races, and also providing reduced friction, high speed capability and enhanced lubrication. Such a bearing would combine the ability of a crossed roller bearing to take a variety of loads in a compact size with the high speed capability of conventional tapered roller bearings. Such a bearing would also have lower friction than conventional crossed roller bearings, resulting in increased bearing life, and would allow longer survival in the event of loss of lubrication.